Mineralogy, geochemistry, and genesis of mudstones in the ... 62/62_4_267.pdfTurkish Petroleum Corporation (TPAO, Ankara, Turkey) using a Rigaku Geigerflex instrument. The XRD analyses

MINERALOGY, GEOCHEMISTRY, AND GENESIS OF MUDSTONES IN THE UPPER

MIOCENE MUSTAFAPAS� A MEMBER OF THE URGUP FORMATION IN THE

CAPPADOCIA REGION, CENTRAL ANATOLIA, TURKEY

TACIT KULAH1, SELAHATTIN KADIR

1 ,* , ALI GUREL2 , MUHSIN EREN

3, AND NERGIS ONALGIL1

1 Eskis� ehir Osmangazi University, Department of Geological Engineering, TR-26480 Eskis� ehir, Turkey2 Nigde University, Department of Geological Engineering, TR-51200 Nigde, Turkey

3 Mersin University, Department of Geological Engineering, TR-33343 Mersin, Turkey

Abstract—The Upper Miocene Mustafapas� a member of the Urgup Formation in the Cappadocia regionconsists predominantly of mudstones, sandstone, and conglomerate lenses with ignimbrite and basaltintercalations. The mudstones are an important source of raw materials for the ceramics industry in Turkey.A detailed mineralogical, geochemical, and genesis study of these materials has not been performedpreviously and the present study aims to fill that gap. The characteristics of mudstones of the Mustafapas� amember were examined using X-ray diffraction, scanning and transmission electron microscopy, energydispersive spectroscopy, and chemical analyses. Weathering products of ophiolitic and pyroclastic rockswere transported into the tectonically subsided zone where they accumulated as fluvial and lacustrinedeposits. Weathering in the mudstones is evidenced by smectite flakes associated with relict pyroxene, rod-like amphibole, feldspar, and volcanic glass. The chemical composition of mudstones and their distributionsuggest that the depositional basin was supplied with ophiolitic material in the south and ignimbritematerial in the north. This interpretation is based on an increase in the quantity of feldspar and opal-A and adecrease in the Fe2O3+MgO/Al2O3+SiO2 ratio from south to north in the study area. The northwardincreases in Light Rare Earth Elements/Heavy Rare Earth Elements, La/Yb, Zr/Ni and Zr/Co ratios and Nb,Ba, Rb, Sr, and Eu in the mudstones of the Mustafapas� a member with positive Eu anomalies suggest thatthe Fe, Mg, Al, and Si required to form smectite were supplied mainly through the decomposition ofamphiboles, pyroxenes, feldspars, and volcanic glass during weathering processes. After the deposition ofmudstones, relative increases in evaporation-controlled Ca, K, and Al in pore water favored the partialdissolution of Ca-bearing minerals and smectite flakes and in situ precipitation of calcite and traces of illitefibers under alkaline micro-environmental conditions during early diagenesis.

Key Words—Cappadocia, Ignimbrite, Mudstone, Ophiolite, Smectite, Turkey, Weathering.

INTRODUCTION

The study area occupies ~400 km2 in the Cappadocia

region in central Anatolia (Turkey), which contains

widespread argillaceous sediments of the Upper

Miocene Mustafapas� a member of the Urgup Formation.

In recent decades, extensive attention to the sedimentol-

ogy, mineralogy, and geochemistry of mudstones has led

to significant advances relating to cement, ceramics, and

shale gas (e.g. Casciello et al., 2011; Chermak and

Schreiber, 2014; Osborn et al., 2014; Taylor and

Macquaker, 2014). Most published studies of the area

are related to volcanism, mineralogy-petrography, and

tectonics (Pasquare, 1968; Pasquare et al., 1988; Batum,

1975, 1978; Innocenti et al., 1975; Besang et al., 1977;

Ercan et al., 1987, 1989; Goncuoglu and Toprak, 1992;

Le Pennec et al., 1994; Druitt et al., 1995; Schumacher

and Mues-Schumacher, 1996; Gevrek, 1997; Turkecan et

al., 2003; Viereck-Gotte and Gurel, 2003; Le Pennec et

al., 2005). Less work has been done on the mineralogy

and distribution of Pliocene clay-rich sediments in

vertical stacked paleosol levels among ignimbrites

(Gurel and Kadir, 2006). The geology and mineralogy

of the Upper Miocene and paleosol and carbonate levels

and their vertical distributions are used as clues to

determine the paleoclimatic conditions of Anatolia and

the Mediterranean region (Gurel and Kadir, 2008; Kadir

et al., 2013; Goz et al., 2014). To date, no detailed study

has been carried out of the mineralogy, geochemistry,

and genesis of these smectitic materials in the Upper

Miocene Mustafapas� a member of the Cappadocia Basin.

The implications of ophiolitic and volcanic sources for

deposits which contain several hundred million tons of

clay reserves of potential raw material (for use in

cement, ceramics, and elsewhere) also need to be

understood. The present study focuses on the mineralogy

and geochemistry of the mudstone of the Mustafapas� amember and associated sediments and interprets the

genetic relationship between argillaceous sediments and

ophiolitic rocks and the Yes� ilhisar conglomerate,

including ophiolitic components and ignimbrites.

* E-mail address of corresponding author:

[email protected]

DOI: 10.1346/CCMN.2014.0620403

Clays and Clay Minerals, Vol. 62, No. 4, 267–285, 2014.

MATERIALS AND METHODS

In the field, representative stratigraphic sections were

measured to study the lateral and vertical variations in

the Mesozoic ophiolitic rocks, the Oligo-Miocene

Yes� ilhisar conglomerate, the mudstone of the Upper

Miocene Mustafapas� a member, and the ignimbrite. One

hundred and seventeen (117) characteristic samples were

collected from these units (Figure 3). Fresh and partially

altered samples were examined under a polarizing

microscope (Leitz Laborlux 11 Pol).

The mineralogical characteristics of the samples were

determined by powder X-ray diffraction (XRD) at the

Turkish Petroleum Corporation (TPAO, Ankara, Turkey)

using a Rigaku Geigerflex instrument. The XRD

analyses were performed using CuKa radiation with a

scanning speed of 1º2y min�1. Randomly oriented

mounts of powdered whole-rock samples were scanned

to determine the mineralogy of each bulk sample.

Samples for clay analyses (<2 mm) were prepared by

separating the clay fraction using sedimentation and

centrifuging the suspension after an overnight dispersion

in distilled water. The clay particles were dispersed

using ultrasonic vibration for ~15 min. Oriented speci-

mens of the <2 mm fractions were prepared from each

sample using the following procedure: drying with air,

solvating with ethylene glycol at 60ºC for 2 h, and

thermal treatment at 550ºC for 2 h. Semi-quantitative

abundances of rock-forming minerals were obtained

using Brindley’s (1980) external standard method. The

relative abundances of clay-mineral fractions were

determined using their basal reflections and the mineral

intensity factors of Moore and Reynolds (1989).

Scanning electron microscopy (SEM) studies were

performed at Eskis� ehir Osmangazi University (Turkey)

using a JEOL JSM 84A instrument equipped with an

EDX detector. Representative clay-dominated bulk

samples were prepared for SEM analyses by adhering

the fresh, broken surface of each sample to an aluminum

sample holder with double-sided tape and coating thinly

(350 A) with gold using a Giko ion coater. Transmission

electron microscopy (TEM) studies were performed at

Anadolu University (Eskis� ehir, Turkey) using a JEOL

JEM-21007 instrument. The clay particles for TEM

analyses were dispersed using an ultrasonic ethanol bath

for ~30 min. One drop of each clay suspension was

placed on carbon-coated copper grids and dried at room

temperature.

Chemical analyses of 29 ophiolite and related

Yes� ilhisar conglomerate, mudstone and ignimbrite

whole-rock samples were performed at Acme

Analytical Laboratories Ltd. (Vancouver, Canada)

using inductively coupled plasma-atomic emission

spectroscopy (ICP-AES) for major and trace elements

and inductively coupled plasma-mass spectrometry

(ICP-MS) for rare-earth elements (REE). The detection

limits for the analyses were between 0.01 and 0.1 wt.%

for major elements, 0.1 and 5 ppm for trace elements,

and 0.01 to 0.5 ppm for REE.

Smectite structural formulae were determined for the

chemical analyses of <2 mm clay fractions of smectite

(confirmed by XRD). The samples were prepared by

separating the clay fraction using sedimentation fol-

lowed by centrifugation of the suspension after an

overnight dispersion in distilled water. They were then

analyzed using ICP-AES at Acme Analyt ical

Laboratories Ltd. (Vancouver, Canada). The structural

formulae of smectite were calculated from chemical

analyses based on the 22 oxygen atom content of the unit

cell (Moore and Reynolds, 1989).

GEOLOGICAL SETTING AND DEPOSITIONAL

ENVIRONMENT

Geological setting

The basement rocks of the Cappadocia region

comprise Mesozoic ophiolitic rocks consisting of

serpentinized peridotites and pyroxenites, isotropic

gabbros, diabasic dikes, and extrusive rocks (Dilek and

Whitney, 1997). The ophiolitic rocks were thrust onto

Paleozoic metamorphic rocks, including gneiss and

marble. The region was later subjected to an extensional

tectonic regime from the Middle Miocene until the Early

Pliocene, which caused the occurrence of a depressional

basin in central Anatolia (Toprak, 1998). This subsided

basin is filled with fluvial and lacustrine sediments and

pyroclastic rocks.

The Oligo-Miocene Yes� ilhisar conglomerate typically

comprises ophiolitic and metamorphic rock fragments

and Neogene sediments. The Yes� ilhisar conglomerate

overlies discordantly the basement rocks (Figures 1 and

2) and is overlain unconformably by Neogene sediments

of the Urgup Formation (Pasquare, 1968). The Upper

Miocene Mustafapas� a member is the oldest sedimentary

unit in the Urgup Formation, which consists of massive

and layered mudstones and conglomerates and sandstones

of fluvial and lacustrine origin. The Mustafapas� a member

overlies ophiolitic basement rocks near the Akkoy and

Kes� lik villages and the Yes� ilhisar conglomerate to the

south of Yes� ilhisar. The sediments of the Mustafapas� amember near the Damsa Valley south of Urgup are

intercalated locally with the Kavak ignimbrite, a welded,

thickly bedded, dark gray Sarımadentepe ignimbrite, and

Damsa Valley basaltic lava. The Mustafapas� a member is

overlain conformably by Late Miocene to Pliocene

volcaniclastic and sedimentary units, which are overlain

discordantly by Quaternary ashfall deposits, white

travertine, and alluvium (Figure 2, Viereck-Gotte et al.,

2010).

Description of the lithology

In the study area, the following lithologies have been

distinguished in the Oligo-Miocene and Upper Miocene

sediments (Figures 3, 4).

268 Kulah et al. Clays and Clay Minerals

Figure 1. Simplified geological map of the Cappadocia region (after Pasquare, 1968).

Vol. 62, No. 4, 2014 Genesis of mudstones in the Mustafapas� a member in Cappadocia 269

Figure 2. Generalized stratigraphic column of the study area (after Viereck-Gotte et al., 2010).


Figure

3.Distributionoftheprincipallithologiesin

thestudyarea(seeFigure

1forsectionlocationsandTable

1forthemineralogicalcompositionsoftheselectedsamples).


Conglomerate. This facies appears in two stratigraphic

levels characterized by thick-bedded fluvial sediments of

the Yes� ilhisar conglomerate (Figure 4a,b) and channel

filling in the mudstone of the Mustafapas� a member. The

Yes� ilhisar conglomerate consists almost entirely of

conglomerates, including ophiolitic and metamorphic

rock fragments. The pebbles are well rounded and their

size varies from a few cm to 20�30 cm. To the north,

metamorphic components predominate in these con-

glomerates. The matrix of the conglomerate consists of

red, sandy, silty, and argillaceous material. This

lithology appears in an area ~40 km long and 10 km

wide. The channel-filling conglomerates in the mudstone

of the Mustafapas� a member are characterized by

massive, gray, unsorted, and sub-rounded conglomer-

ates. The conglomerates are mainly matrix-supported.

The average size of the clasts is ~10 cm. The thickness

of the conglomerate varies from 20 to 50 cm. This

conglomerate channel has a lenticular character with a

cross-section ~2 m wide.

Sandstone. This facies consists of greenish-gray, medium-

to fine-grained, medium-bedded sandstones with plant

rootlets. The facies is ~50 cm thick and several km long.

Mudstone. This massive and layered mudstone facies

appears in two stratigraphic levels characterized by

different colors (Figure 4c,d). The lower level is

generally greenish-gray, but the upper level is brown-

ish-red. The facies includes plant rootlets and desicca-

tion cracks. The mudstone is ~70 m thick, 10 km wide,

and 60 km long.

Description of stratigraphic sections

Eight stratigraphic sections were analyzed from south

to north in the study area, and the results are described

below (Figure 3, K1�K8).

Hacibekirli section (K1). The Yes� ilhisar conglomerate

unconformably overlies the Cukurbag Formation, which

is overlain by the Cemilkoy ignimbrite (Gurel et al.,

Figure 4. Field view of: (a) the weathered ophiolitic unit and the overlying Yes� ilhisar conglomerate; (b) close-up view of ophiolite-

sourced pebbles in a matrix of mudstone in the Yes� ilhisar conglomerate; (c) mudstone of the Mustafapas� a member on the weathered

ophiolitic units; and (d) close-up view of theMustafapas� a mudstone with intercalated sandstone lenses and overlain by the Cemilkoy

ignimbrite.


2007; Figure 3). The section consists predominantly of

ophiolitic conglomerate and sandstone and mudstone

horizons. These units are overlain by the Cemilkoy

ignimbrite.

Araplı Pass section (K2). This section begins with the

Yes� ilhisar conglomerate, which overlies unconformably

ophiolitic rocks and is overlain unconformably by

mudstones, sandstones, and conglomerates of the

Mustafapas� a member (Figure 4a). The Yes� ilhisar con-

glomerate consists of pebbles and cobbles derived

predominantly from ophiolitic basement rocks, such as

gabbro, pyroxenite, and serpentinite and minor amounts

of marble and gneiss (Figure 4b). This section is covered

by the Cemilkoy ignimbrite.

Araplı section (K3). The ophiolitic basement rocks show

signs of weathering. This unit is overlain unconformably

by the Mustafapas� a member deposits which consist of

mudstones intercalated with sandstones and conglomer-

ate lenses (Figure 4c). The Cemilkoy ignimbrite occurs

in the uppermost part of this section (Figure 4d).

Yes� ilhisar section (K4). This section begins with an

ophiolitic unit that is overlain unconformably by the

Yes� ilhisar conglomerate, which is overlain unconform-

ably by the sediments of the Mustafapas� a member. This

section is covered by the Cemilkoy ignimbrite.

Cevliktas� Tepe section and Akkoy section (K5, K6). The

ophiolitic basement rocks are overlain unconformably,

mainly by mudstone deposits of the Mustafapas� amember, which is overlain by the Cemilkoy ignimbrite.

Kolkollu Tepe section (K7). This section begins with the

Sarımadentepe ignimbrite, which is overlain by

Mustafapas� a member sediments and topped by the

Cemilkoy ignimbrite. The thicknesses and frequency of

occurrence of conglomerate lenses in the Mustafapas� amember are less than in the southern area. A reddish

color is predominant in the Mustafapas� a-member sedi-

ments compared with those of previously described

sections.

Mustafapas� a section (K9). This section begins with the

Kavak ignimbrite, which is overlain by Mustafapas� a-member sediments composed of mudstones intercalated

with sandstone and conglomerate lenses and the

Sarımadentepe ignimbrite. This section is topped by

the Damsa Valley basalt.

PALEOGEOGRAPHY

Tectonic activity during the Oligocene caused the

uplift and emergence of the region, after which

ophiolitic basement rocks and ignimbrites were sub-

jected to moderate to intensive weathering. Weathering

products were eroded, transported, and deposited in the

subsided basin. The Yes� ilhisar conglomerate, consisting

mainly of ophiolitic components, was deposited close to

the source area in these valleys. Thin lacustrine

sediments were deposited in areas to the north.

Polygenetic volcanoes were active in the Late Miocene

and their pyroclastic products, such as the Kavak and

Sarımadentepe ignimbrites, were intercalated with mud-

stones in the northern part of the study area (Pasquare,

1988; Toprak, 1998; Le Pennec et al., 2005). During the

arid climatic conditions at the beginning of the Late

Miocene, the lacustrine areas were subjected to flash

flooding, which caused the deposition of mud and the

development of mud flats. Argillaceous sediments then

formed in the region (Kadir et al., 2013). According to

the profiles examined, the main lithofacies consist of

massive and layered mudstones, which occur in three

sections: the very shallow part of the lake (southern lake

margin, Figure 3, K1, K2), the central part of study area

around Akkoy (Figure 3, K3, K4, P5, K6), and a

shallow-lake environment (north, Figure 3, K7, K8). In

the depressional basin, the main paleo-flow direction

was generally determined to have been from south to

north, based on field observations such as pebble

orientation, planar and trough cross-beddings in sand-

stones, and the mineralogical compositions of detrital

sediments.

RESULTS

Mineralogical and petrographical determinations

Ophiolitic rocks are generally composed of serpenti-

nized amphibole, pyroxene, and accessory olivine (Dilek

and Furnes, 2014). The Yes� ilhisar conglomerate includes

components derived mainly from basement rocks. These

components consist of serpentinized and Fe (oxyhydr)-

oxide-bearing amphibole, pyroxene, and olivine miner-

als with partial to extensive alteration (Nahon et al.,

1982; Delvigne, 1998). Volcanic rocks include plagio-

clase and amphibole phenocrysts in a volcanic glass

groundmass. Feldspars and amphiboles are altered, and

the volcanic glass is devitrified.

The XRD results of the bulk samples from the

measured profiles are given in Table 1. Smectite is

dominant in all of the samples from the sections of the

Mustafapas� a member and is accompanied by feldspars,

quartz, amphiboles, pyroxenes, calcite, local olivine, and

traces of illite/mica, kaolinite, chlorite, and serpentine.

The quantities of feldspar and opal-A increase from

south to north in the study area.

Smectite is identified by a sharp basal reflection at

14.48�14.91 A, which shifts to 17.51�17.65 A follow-

ing ethylene-glycol treatment and collapses to

10.08�10.13 A after heating at 550ºC for 2 h

(Figure 5). The d060 value of smectite is 1.50 A,

suggesting a dioctahedral character (Moore and

Reynolds, 1989). Illite/mica is identified by reflections


Table 1. Mineralogical composition and abundance of samples in the measured sections. Sections and their samples areordered from north to south.

Sample Rock type smc ilt/mc kln chl srp am px ol fds qz op cal

NorthK8MP2-22 Mudstone ++++ acc acc + acc accMP2-21 Mudstone +++ acc acc acc + + +MP2-20 Mudstone +++ + + +MP2-16 Mudstone +++ acc + + accMP2-14 Mudstone +++ acc acc + + +MP2-10 Mudstone +++ acc + acc + acc +MP2-7 Mudstone + acc +++ acc + accMP2-4 Mudstone +++ acc acc + acc +MP2-3 Mudstone ++ acc acc ++ acc accK7KT2-1 Mudstone +++ acc + + +KT2-2 Mudstone +++ acc ++ + +KT2-3 Mudstone +++ + +++ + accKT2-5 Mudstone ++++ acc acc ++ acc +KT2-7 Mudstone ++++ acc acc + acc +KT2-8 Mudstone ++++ acc + acc accKT2-10 Mudstone +++ acc acc acc +KT2-11 Mudstone +++ + acc + acc

MiddleK6AKB-11 Mudstone ++++ acc + +AKB-10 Mudstone ++++ acc + +AKB-9 Mudstone ++ acc acc + ++AKB-7 Mudstone +++ acc + acc + acc +AKB-5 Mudstone ++ acc acc acc + ++AKB-4 Mudstone ++ acc acc + + + ++K5C-2 Mudstone +++ acc acc acc + + accC-3 Mudstone +++ acc + acc +C-4 Mudstone ++ acc acc + + ++C-5 Mudstone ++ acc + + +K4YH-2 Mudstone ++ acc acc acc + + acc ++YH-5 Mudstone ++ acc acc + +YH-7 Mudstone ++ acc acc + acc + +YH-10 Mudstone ++ acc acc acc + + +YH-11 Mudstone ++ acc + acc + + acc accYH-13 Mudstone +++ acc acc + acc + acc ++K3AT-5 Mudstone +++ acc acc + +AT-8 Mudstone ++ + + acc

SouthK2A22N-11 Mudstone ++++ acc +A22N-4 Mudstone ++++ +K1HB-2 Mudstone +++ acc +

HB-3 Matrix of Yes� ilhisarconglomerate

++++ acc acc acc + acc

HB-5 Mudstone ++++ acc acc acc + acc

smc: smectite, ilt/mc: illite/mica, kln: kaolinite, chl: chlorite, srp: serpentine, am: amphibole, px: pyroxene, ol: olivine; fds:feldspar, qz: quartz, op: opal-A, cal: calcite. acc: accessory, +: relative abundance of mineral.


at 10.0 and 5.0 A, which are not affected by the

ethylene-glycol treatment but undergo a slight shift

toward a higher angle when heated to 550ºC because of

dehydroxylation. Kaolinite has peaks at 7.24 and 3.57 A

and serpentine has peaks at 7.63 A. Sharp peaks appear

in amphibole at 8.36 and 3.11 A, in pyroxene at 2.90 A,

in olivine at 2.80 A, in quartz at 3.34 and 4.26 A, in

feldspar at 3.18 A, and in calcite at 3.03 A. An increase

in the XRD background intensity in some of the samples

may indicate the presence of opal-A (Iijima and Tada,

1981).

Amphibole is associated with accessory chlorite,

serpentine, and olivine and is found mainly in weathered

ophiolitic units, related to weathered units of the Araplı

area in the southern region of the studied area. Illite and

feldspar increase northward near the Akkoy area.

Figure 5. XRD patterns of smectite-rich mudstone samples (YH-11, YH-13, AKB-10). smc: smectite, kln: kaolinite, fds: feldspar,

qz: quartz, am: amphibole, ol: olivine, cal: calcite.


SEM-EDX AND TEM DETERMINATIONS

Scanning electron microscope images indicate that

flaky smectite predominates in the mudstone and matrix

of the Yes� ilhisar conglomerate samples (Figure 6). Flaky

smectite crystals (up to 2�7 mm in diameter) appear in

the samples with irregular outlines and are locally edged

with fibrous illite (Figure 6a�h). Amphiboles with rod-

like forms (~10 mm long) and pyroxene relics are

associated with smectite in the mudstones from the

southern part of the study area (Figure 6c,d). Smectite in

the northern mudstones occur as authigenic flakes and

include relict crystals, such as feldspar and devitrified

volcanic glass (Figure 6e,f). In addition, irregular flaky

smectite in the central mudstone encloses authigenic

euhedral micritic calcite crystals (1�7 mm in diameter)

as regular pore fillings (Figure 6g,h).

Energy dispersive analyses of the smectite flakes

have large peaks for Si, Al, Fe, and Ca and low Al and

Mg (Figure 7a). Energy dispersive analyses of rod and

rod-bundle amphibole crystals yielded Si, Ca, and Fe

and low Al, whereas the pyroxene precursor exhibits

high Ca, Fe, and Si and low Mg resembling augite-type

pyroxenes (Figure 7b,c). Relics of feldspars exhibit high

peaks for Si, smaller peaks for Al, and very faint peaks

for K and Ca (Figure 7d). The altered volcanic rocks

consist mainly of Si with very small peaks for Al, Mg, K,

Ca, and Na (Figure 7e). Rhombic calcite crystals exhibit

strong peaks for Ca (Figure 7f).

Transmission electron microscope analyses indicate

that the smectite particles occur as wavy fan- and lens-like

plate packets arranged in a well oriented order

(Figure 8a�f). In addition, there are discontinuous, bent

and non-oriented packs of smecti te part ic les

(Figure 8b�f). Smectite plates edge rod-like crystals of

amphiboles in the mudstones (Figure 8d�f). The sharp

edges of the individual fibers suggest moderate to high

crystallinity. The smectite plates have a diameter of

300�600 nm.

Geochemistry

Chemical analyses of representative samples of

ophiolite and the associated Yes� ilhisar conglomerate

matrix, mudstones, and ignimbrites in the Cappodocia

region are given in Table 2 (please see an extended

version of this table which has been deposited with the

Editor in Chief and is available from http://www.clays.

org/JOURNAL/JournalDeposits.html). The variations in

the major and trace-element profiles appear to be related

to ophiolitic and volcanic provenances (Table 2, plus

extended version, deposited). Therefore, SiO2, K2O,

TiO2, SREE, and Zr values increase and Fe2O3 and MgO

values decrease northward in the mudstones of the

Mustafapas� a member. The loss on ignition is an

important indicator of weathering and is proportional

to the amount of calcite and clay minerals. Large

amounts of Cr, Ni, and Co are found in the ophiolitic

rocks with average values of 1850, 1917, and 98.5 ppm,

respectively. The Cr, Ni, and Co contents decrease from

the south to the middle to the north with average values

in the mudstones of the Mustafapas� a member of 548,

475, and 40 ppm; 402, 226, and 26 ppm; and 136, 46,

and 15 ppm, respectively. In addition, the Ba, Rb, and Sr

contents of the sediments of the Mustafapas� a member

display local increases northward.

SiO2 has a positive correlation with K2O, and SREEcorrelates positively with Zr in the mudstone samples

(Figure 9a,b). A plot of Zr/Ni vs. Zr/Co shows a

northward increase in Zr content relative to Ni and Co

(Figure 10).

The whole-rock REE contents of samples from the

study area were normalized to the North American Shale

Composite (NASC) values (Gromet et al., 1984)

(Figure 11). Light REEs (LREEs), such as La, Ce, and

Nd, are enriched relative to the increase in concentrations

of medium REEs (MREEs) and heavy REEs (HREEs)

based on the increase in LaN/YbN ratios from 0.41 to 5.96

in mudstones from south to north in the study area

(Table 1, Figure 11a�c). However, LREEs were leached

relative to the MREEs and HREEs in mudstone samples

close to the ophiolitic units and related Yes� ilhisarconglomerates in the southern region (Table 1, Figure

11a,d). Nb/Ti increases parallel to the increase in La/Yb

northward (Figure 12). The LREE/HREE ratio is enriched

in ignimbrite samples (Figure 11e).

The averages [(Eu/Eu*)NASC= 0.98�1.67 and

(Ce/Ce*)NASC = 0.75�1.06] show positive Eu and

negative Ce anomaly values, respectively (Table 2,

deposited). The (Yb/Yb*)NASC ratios range from 0.80

to 1.17 and are positive, revealing a relatively immobile

character.

The structural formulae of smectite were calculated

from chemical analyses of the clay fractions of samples

A22N-11, AKB-11, and KT2-8 (Table 3). The average

structural formula was estimated to be (Si7.59Al0.41)

(Al2.34Fe0.93Mg0.76Ti0.06Mn0.013)(Ca0.29Na0.03K0.20)

O20(OH)4. The tetrahedral site is filled by Si, which is

substituted by a small amount of Al. Al is the

predominant cation in the octahedral site and is

accompanied by Fe3+, Mg, and traces of Ti and Mn.

Ca, Na, and K were deemed exchangeable interlayer

cations. The average tetrahedral charge/octahedral

charge ratio (xt/xo) is 1.00. These values indicate that

the smectite is montmorillonite, similar to that reported

by Guven (1988) and Inoue et al. (2004).

DISCUSSION

The basement rocks in the study area consist of

Paleozoic and Mesozoic gneiss, marble, and ophiolitic

rocks. Long-term weathering of ophiolite and ignimbrite

units from the Early Eocene to the Late Miocene produced

an enormous amount of argillaceous material that was

later transported and deposited in the depressional basin


Figure 6. SEM images: (a,b) irregular cornflake-shaped smectite in southern mudstones (YH11, A22N-11); (c) smectite flakes with

rod-like amphibole crystals (YH-13); (d) altered pyroxene edging smectite flakes (KT2-8); (e,f) authigenic growth of smectite on

and between altered feldspar crystals and devitrified volcanic glass (AKB-13); (g,h) authigenic growth of calcite crystals in pores of

irregular smectite and smectite-edged illite (AKB-8).


as fluvial and lacustrine deposits. Evidence of weathering

is seen in smectite flakes in the mudstones, which are

associated with relict pyroxenes, rod-like amphiboles,

feldspars, and volcanic glass (Figure 6). The suggestion of

a detrital origin for the smectitic mudstone is based

mainly on its repetition in stratigraphic sections and its

matrix form in conglomerates, associated discrete miner-

als derived from ophiolitic and volcanogenic rocks (Hong

et al., 2007, 2012) and micromorphologies of smectite

flakes with irregular boundaries.

Changes in the concentrations of Fe2O3+MgO,

Al2O3, and SiO2 in the mudstones of the Mustafapas� amember are caused by vertical and lateral variations in

lithologies. The presence of Fe2O3+MgO in the sedi-

ments may indicate detrital pyroxene, amphibole, and Fe

(oxyhydr)oxide phases from ultramafic units exposed in

the south and SiO2 and Al2O3 from volcanogenic

materials, such as feldspars and opal-A in the northern

region. Therefore, smectitic mudstones from the south-

ern region contain more Fe�Mg and less Si�Al and

Ca+K+Na than either the middle or northern parts

(Table 3). After the deposition of smectitic mudstones,

the local concentration of Ca and K (along with Al) in

the pore water resulted in in situ formation of calcite

cement filling the micropores.

The edging of irregular smectite flakes by trace illite

developed as a result of a dissolution and precipitation

mechanism under alkaline micro-environmental condi-

tions during early diagenesis (Braide and Huff, 1986;

Erhenberg, 1991; Meunier and Velde, 2004; Ziegler,

2006). The presence of trace kaolinite in the northern

part was caused by the relative increase of altered

feldspars, amphiboles, and volcanic glass in the volcanic

input throughout the sequence.

Figure 7. EDX analyses of smectite and precursors in mudstone samples.


Figure 8. TEM images showing: (a) smectite plates, plate bundles (A22N-11); (b�d) wavy fan- and lens-like smectite plate packets

(A22N-11, AKB-11); (d�f) smectite plates edging rod-like amphiboles (AKB-11), and (c�d) smectite plates edging fibrous

materials resembling illite (A22N-11, AKB-11).


Table 2. Major oxides (wt.%), trace elements (ppm), and REE contents (ppm) of ophiolite, the Yes� ilhisar conglomerate matrix,mudstones, and ignimbrites in the study area.

Major oxides(wt.%)

OphioliteYes� ilhisarmatrix

————— Mudstone —————— Ignimbrite

South Middle NorthAvg. (n = 3) (n = 1) Avg. (n = 4) Avg. (n = 11) Avg. (n = 8) Avg. (n = 2)

SiO2 39.04 58.57 50.35 44.70 57.87 70.2Al2O3 1.1 19.04 16.95 11.70 15.22 14.29SFe2O3 8.05 4.58 9.12 6.23 6.11 1.73MgO 36.51 2.15 4.38 4.24 1.57 0.39CaO 0.16 1.26 2.71 11.68 3.1 1.76Na2O 0.003 1.83 2.09 1.24 1.57 2.33K2O – 0.41 0.56 0.92 1.74 3.64TiO2 0.006 0.68 0.50 0.58 0.56 0.26P2O5 – 0.02 0.04 0.08 0.11 0.03MnO 0.07 0.02 0.07 0.09 0.06 0.05LOI 13.8 11.2 13.2 18.3 12.0 5.2

Total 99.37 99.88 99.86 99.84 99.83 99.90

Trace elements (ppm)Ba 5 61 50.25 144.3 609 760.5Be 0.33 2 1 1.7 1.5 2Co 98.53 34.8 40.05 26 14.8 3.5Cr 1850 590 547.5 401.8 136.25 80Cs – 0.9 3.43 6.3 3.4 4.9Ga 0.73 17.3 13.48 10.9 14.2 13.5Hf – 2.4 1.4 2.3 3.8 4.2Nb – 2.6 3.1 6 8.8 4.2Ni 1917 567 474.8 226.3 46 34Rb 0.16 10.4 29.3 42.3 76.4 122.8Sc 8 44 27.5 18.3 12.1 3.5Sn 0.33 – – 0.4 0.6 –Sr 5 72.2 100.4 216.3 222.3 217.4Ta – 0.2 0.26 0.4 0.6 0.9Th – 1.5 1.9 5.4 12.7 21.9U 0.3 0.4 1.9 1.6 2.6 6.45V 37.3 255 127.5 109 72 5.5W 0.43 – 1.05 1.6 2.2 2.7Zr 0.4 77.1 51.2 85.2 145.7 148Y 0.2 38.9 10.25 15.4 19.5 15.6La 0.13 9.8 4.7 15.1 24.6 36.9Ce 0.13 26.1 10.3 26.7 44.4 60.4Pr – 3.87 1.17 3.29 4.87 5.93Nd – 19.5 5.33 12.7 17.8 20Sm – 5.82 1.29 2.63 3.20 3.05Eu – 1.96 0.42 0.73 0.85 0.64Gd – 7.26 1.58 2.65 3.10 2.6Tb – 1.23 0.26 0.42 0.50 0.39Dy – 7.30 1.77 2.73 3.20 2.44Ho – 1.52 0.37 0.55 0.68 0.52Er – 4.62 1.09 1.56 1.93 1.59Tm – 0.60 0.16 0.22 0.30 0.26Yb 0.23 3.77 1.16 1.55 2.16 1.89Lu – 0.56 0.18 0.23 0.34 0.29TOT/C 0.1 0.03 0.24 2.42 0.26 0.15TOT/S – 0.03 0.25 0.04 0.004 –Mo 0.07 0.2 0.9 0.3 0.2 1.5Cu 12.73 30.3 56.46 24.8 13.0 3.3Pb 0.33 3.2 3.8 8.24 5.8 1.7Zn 18.3 52 52.5 38.6 19.5 7.5Ni 2017.8 377.3 315.7 204.0 20.7 32.7As 3.1 4.7 8.1 6.9 14.8 –Cd – – – 0.05 – –Sb – – 0.05 0.12 0.03 –


The LREEs/HREEs in a NASC-normalized pattern

and the (La/Yb)N ratios are correlated positively with the

concentration of smectite in the mudstone deposits and

increase from south to north, indicating an increasing

contribution of volcanic materials in that direction.

Therefore, the fractionation of amphibole and feldspar

resulted in the adsorption of LREEs onto the smectite

and Fe (oxyhydr)oxide phases, similar to that reported

by Christidis (1998) and Jeans et al. (2000). However,

the depletion of LREEs relative to MREEs and HREEs in

mudstones from the southern region suggests that they

benefited from the alteration of amphibole and pyroxene

that originated from the ophiolitic basement rock

(Cullers and Graf, 1983; Nyakairu and Koeberl, 2001).

A positive Eu anomaly value suggests that the accumu-

lation and alteration of plagioclase originated from the

input of interlayered volcanic units (Nance and Taylor,

1977).

The parallel northward increase in the Nb/Ti abun-

dance ratio relative to the La/Yb ratio suggests that Nb

and La are concentrated with increasing smectite-

dominated mudstone deposits derived mainly from

ophiolite and related Yes� ilhisar conglomerates and

volcanic source rocks. This was confirmed by a north-

ward parallel increase in the Zr/Ni ratio relative to the

Zr/Co ratio and a positive correlation of Zr with SREEin the mudstone samples. This suggests that SREE have

a similar geochemical behavior associated with the

molecular structure of smectite, which increases north-

ward with Zr. This interpretation is also supported by an

increase in Ba, Rb, and Sr in the mudstones of the

Mustafapas� a member to the north, close to the Kavak

and Sarımadentepe ignimbrites, and by the increase in

Ni, Co, and Cr in the mudstones in the south, near the

ophiolitic basement units. Intermediate values of these

data are present in the mudstones in the middle area.

Table 2 (contd.)

Major oxides(wt. %)

OphioliteYes� ilhisarmatrix

————— Mudstone —————— Ignimbrite

South Middle NorthAvg. (n = 3) (n = 1) Avg. (n = 4) Avg. (n = 11) Avg. (n = 8) Avg. (n = 2)

Bi – – 0.05 0.07 0.11 0.05Ag – – – – – –Au (ppb) 2.6 – 0.9 1.2 1.5 1.2Hg 0.003 – 0.02 0.02 0.001 –Tl – – – 0.08 0.1 –Se – 0.6 – – 0.01 –SREE 0.69 132.8 40.03 86.46 127.4 152.5SLREE 0.26 59.27 21.50 59.40 91.70 123.2SMREE 0.2 25.09 5.69 9.71 11.5 10.4SHREE 0.1 9.55 2.59 5.45 4.73 4.82Eu/Eu* 1.75 1.30 1.26 1.26 1.20 1.04Ce/Ce* 0.63 0.89 0.92 0.83 0.87 0.97Yb/Yb* 0.89 1.02 1.09 1.09 1.06 1.32LaN/YbN 0.3 0.25 0.41 0.94 5.96 14.42

n: number of samples.SREE = the sum of (La�Lu)+Y; SLREE = the sum of La�Nd; SMREE = the sum of (Sm�Ho); SHREE = the sum of(Er�Lu); Ce/Ce*= 2CeN/(LaN+PrN), Eu/Eu* = 2EuN/(SmN+GdN), Yb/Yb* = 2YbN/(TmN+LuN), where N refers to a NASC-normalized value (Gromet et al., 1984).

Figure 9. Elemental variation diagrams for major oxides (wt.%) and trace elements of the Cappadocia region samples: (a) SiO2 vs.

K2O; (b) Zr vs. SREE.


Figure 10. Plots of Zr/Ni vs. Zr/Co for the smectite-dominated mudstone samples from the south, middle, and north of the study area.

Figure 11. NASC-normalized REE patterns (Gromet et al., 1984) from the smectite-dominated mudstone samples from: (a) the

south; (b) the middle; (c) the north, and (d,e) north of the study area.


Figure 12. Plots of La/Nb vs.Nb/Ti for the smectite-dominated mudstone samples from the south, middle, and north of the study area.

Table 3. Chemical compositions (wt.%) and structural formulae for pure smectite samples.

Major oxides A22N-11 AKB-11 KT2-8 Average(wt.%) South Middle North

SiO2 49.20 50.93 51.0 50.38Al2O3 15.30 15.80 15.30 15.47SFe2O3 11.08 6.19 7.31 8.20MgO 2.84 4.09 3.17 3.37CaO 1.62 1.58 2.20 1.80Na2O 0.03 0.07 0.18 0.09K2O 0.84 1.42 0.94 1.07MnO 0.06 0.10 0.07 0.08TiO2 0.42 0.53 0.59 0.51LOI 18.2 19.0 19.0 18.73Total 99.59 99.71 99.76 99.69SiO2/Al2O3 3.22 3.22 3.33 3.26

TetrahedralSi 7.45 7.65 7.68 7.59Al 0.55 0.35 0.32 0.41S 8.00 8.00 8.00 8.00

OctahedralAl 2.18 2.45 2.39 2.34Fe 1.26 0.70 0.83 0.93Mg 0.65 0.92 0.72 0.76Ti 0.05 0.06 0.07 0.06Mn 0.009 0.02 0.01 0.013S 4.15 4.15 4.02 4.11

InterlayerCa 0.262 0.254 0.355 0.29Na 0.009 0.01 0.052 0.03K 0.162 0.272 0.180 0.20S 0.433 0.536 0.587 0.52

Tetrahedralcharge

0.550 0.350 0.320 0.41

Octahedralcharge

0.170 0.450 0.610 0.41

Total charge 0.720 0.800 0.930 0.82Interlayer charge 0.690 0.800 0.930 0.81xt/xo 3.24 0.78 0.52 1.00

xt/xo = tetrahedral charge/octahedral charge ratio.


However, a slight to moderate negative Ce anomaly in

mudstones and ophiolites suggests the substitution of Ce

by Fe in iron-oxide/hydroxide phases under oxidizing

and reducing sedimentation environments (Fulignati et

al., 1999; Karakaya, 2009; Zhou et al., 2013). This

suggestion was supported by the alternation of green,

yellow, and dark red mudstones, reflecting the fluctua-

tion of reducing and oxidizing conditions in the

depositional environment (Eren and Kadir, 2013).

CONCLUSIONS

The development of flaky smectite and smectite �

illite with relict pyroxenes, amphiboles, feldspars, and

volcanic glass suggests that the weathering of ophiolitic

units in the south and volcanic units in the north

contributed to the accumulation of detrital smectite-

dominated fluvial and lacustrine mudstone deposits of

the Mustafapas� a member in a tectonic depressional

basin. Serpentinized and Fe (oxyhydr)oxide-bearing

pyroxenes and amphiboles, and the alteration of

feldspars, originated from the weathering of ophiolitic

units, related Yes� ilhisar conglomerates, and ignimbrites.

Increases in the LREEs/HREEs, (La/Yb)N, Zr/Ni, and Zr/

Co ratios and Ba, Rb, and Sr in the mudstones in the

northern Mustafapas� a member with a positive Eu

anomaly suggest that the decomposition of detrital

materials from ophiolitic and volcanogenic material

were the main sources of Fe�Mg, Al, and Si for the

smectite in mudstones in the study area. Therefore, the

change in the chemical composition of smectite fractions

in the depressional basin is related mainly to the

proximity to the source area.

ACKNOWLEDGMENTS

The present study was supported financially by theScientific Research Projects Fund of Eskis� ehir OsmangaziUniversity in the framework of Project 201015030 andconstitutes part of the PhD thesis of the first author. Theauthors are much indebted to anonymous reviewers fortheir extremely careful and constructive reviews whichimproved the quality of the paper significantly. Theauthors are also grateful to Associate Editor, Warren D.Huff, and Editor in Chief, Michael A. Velbel, for theirinsightful editorial comments and suggestions.

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